The weevils (Coleoptera: Curculionoidea) from South America are currently classified in the following families and subfamilies: Nemonychidae (Rhinorhynchinae), Anthribidae (Anthribinae), Belidae (Belinae and Oxycoryninae), Attelabidae (Attelabinae and Rhynchitinae), Brentidae (Apioninae and Brentinae), Caridae (Carinae) and Curculionidae (Erirhininae, Dryophthorinae, Entiminae, Aterpinae, Gonipterinae, Rhythirrininae, Thecesterninae, Eugnominae, Hyperinae, Curculioninae, Cryptorhynchinae, Mesoptiliinae (= Magdalidinae), Molytinae, Baridinae, Lixinae, Conoderinae (= Zygopinae), Cossoninae, Scolytinae and Platypodinae). In the present contribution we bring a dichotomous key for the identification of seven families and 28 subfamilies of Curculionoidea from South America, and for 21 tribes of the highly heterogeneous subfamilies Curculioninae and Molytinae. These tribes are Curculionini Anthonomini, Ceutorhynchini, Derelomini, Otidocephalini, Erodiscini, Camarotini, Piazorhinini, Prionobrachiini, Smicronychini, Rhamphini and Tychiini, within Curculioninae; and Hylobiini, Pissodini, Conotrachelini, Cleogonini, Sternechini, Pacholenini, Cholini, Petalochilini and Amalactini, within Molytinae. Most of them have been classified as subfamilies in traditional schemes. The key is mainly based on external morphological characters, but also includes data on genitalia, mouth parts and other biological features. Definitions and illustrations of diagnostic characters used in the key are provided